[gradsusr] MODIS AEROSOL PRODUCTS

[Jennifer Adams]

If a netcdf file doesn't have a time dimension, GrADS will assign a default time of 00z01jan0001 to the file. That message is not an error, it is a warning -- the file was opened successfully. If you want the default time to be something else, use a simple xdfopen-style descriptor to assign a time. If you want to merge files over the time dimension, you can use templating with the CHSUB option -- mapping each file to its particular time -- the strings in the filenames are not readily interpreted, so the usual date string substitutions won't work. 

http://iges.org/grads/gadoc/SDFdescriptorfile.html
http://iges.org/grads/gadoc/templates.html

--Jennifer

On May 29, 2013, at 8:08 AM, Joshua Ngaina wrote:

> 
> Dear All,
> 
> I have daily MODIS aerosol products (Small mode fraction). 
> 
> I wanted to merge these files using CDO but it seemed the files were not merged.  
> 
> met at met-HP-Compaq-6000-Pro-MT-PC:/media/BERTH/MODIS_DAILY$ cdo mergetime *.nc ALLMOD08.nc
> cdo mergetime: Processed 4147200 values from 64 variables over 32 timesteps. ( 0.18s )
> 
> So to check one of the files, I used grads and I got this error: DF file has no discernable time coordinate -- using default values. 
> 
> ga-> sdfopen MOD08_D3.A2001001.051.2010286151047.pscs_000500504418.Optical_Depth_Ratio_Small_Land_And_Ocean_Mean.G3.nc
> Scanning self-describing file:  MOD08_D3.A2001001.051.2010286151047.pscs_000500504418.Optical_Depth_Ratio_Small_Land_And_Ocean_Mean.G3.nc
> SDF file has no discernable time coordinate -- using default values.
> SDF file MOD08_D3.A2001001.051.2010286151047.pscs_000500504418.Optical_Depth_Ratio_Small_Land_And_Ocean_Mean.G3.nc is open as file 1
> LON set to 0 360 
> LAT set to -89.5 89.5 
> LEV set to 0 0 
> Time values set: 1:1:1:0 1:1:1:0 
> E set to 1 1 
> ga-> q file
> File 1 : 
>   Descriptor: MOD08_D3.A2001001.051.2010286151047.pscs_000500504418.Optical_Depth_Ratio_Small_Land_And_Ocean_Mean.G3.nc
>   Binary: MOD08_D3.A2001001.051.2010286151047.pscs_000500504418.Optical_Depth_Ratio_Small_Land_And_Ocean_Mean.G3.nc
>   Type = Gridded
>   Xsize = 360  Ysize = 180  Zsize = 1  Tsize = 1  Esize = 1
>   Number of Variables = 2
>      optical_depth_l  0  y,x  Aerosol Optical Thickness at 0.55 microns for both Ocean (best) and Land (corrected): Mean
>      optical_depth_r  0  y,x  Ratio of small mode aerosol optical depth at 0.55 micron for both land and ocean: Mean
> 
> I also checked the merged netcdf file 
> 
> ga-> sdfopen ALLMOD08.nc 
> Scanning self-describing file:  ALLMOD08.nc
> SDF file has no discernable time coordinate -- using default values.
> SDF file ALLMOD08.nc is open as file 1
> LON set to 0 360 
> LAT set to -89.5 89.5 
> LEV set to 0 0 
> Time values set: 1:1:1:0 1:1:1:0 
> E set to 1 1 
> ga-> q file
> File 1 : 
>   Descriptor: ALLMOD08.nc
>   Binary: ALLMOD08.nc
>   Type = Gridded
>   Xsize = 360  Ysize = 180  Zsize = 1  Tsize = 1  Esize = 1
>   Number of Variables = 2
>      optical_depth_l  0  y,x  Aerosol Optical Thickness at 0.55 microns for both Ocean (best) and Land (corrected): Mean
>      optical_depth_r  0  y,x  Ratio of small mode aerosol optical depth at 0.55 micron for both land and ocean: Mean
> 
> I also noted that the dimension of both files were the same. 
> 
> My major problem is with many files of this type, How do I merge this files for analysis with GrADs. Please advise
> 
> 
> Regards and Thanks,
> 
> Joshua Ngaina
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--
Jennifer M. Adams
IGES/COLA
4041 Powder Mill Road, Suite 302
Calverton, MD 20705
jma at cola.iges.org



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